The overall aim of this study is to determin whether subclinical myocardial damage can be detected in children. Also to determine whether a detectable elevation of serum cardiac troponin I occurs in children with high likelihood of myocardial cell damage; and the conditions under which this elevation occurs. To correlate elevations in serum cardiac troponin I with other indicators of my- ocardial damage and to determine if these levels can be used during childhood to detect myocyte damage, and to establish the pediatric baseline level.